Steam engine compounding (Woolf type): mechanical arrangement In a Woolf-type compound engine used in steam practice, how are the high-pressure (HP) and low-pressure (LP) cylinders mechanically connected and arranged with respect to their pistons and rods?

Introduction / Context:
The Woolf-type compound engine is a classic configuration in which steam expands in two stages: first in a high-pressure (HP) cylinder and then in a low-pressure (LP) cylinder. Understanding its distinctive mechanical linkage helps students differentiate it from cross-compound and tandem-compound layouts, which affects torque smoothness, footprint, and maintenance.

Given Data / Assumptions:

• The question concerns the mechanical connection between HP and LP cylinders.
• Woolf compound engines are intended for two-stage expansion on a common axis.
• No numerical data is required; this is a conceptual design-identification item.

Concept / Approach:
Woolf compounding is essentially a tandem arrangement: the HP and LP pistons act in line on the same piston rod. Steam exhausts from the HP cylinder directly into the LP cylinder (sometimes via a minimal receiver), keeping the assembly compact and ensuring axial alignment of forces.

Step-by-Step Solution:
Identify Woolf type as tandem compounding.In a tandem engine, HP and LP cylinders are in line and act on a common rod and common crank.Therefore the pistons share the same piston rod; they are not mounted with separate cranks at 90° (that would be cross-compound).Conclude that the correct mechanical connection is a common piston rod.

Verification / Alternative check:
Historic diagrams of Woolf engines show the HP cylinder mounted ahead of the LP cylinder on the same axis, both attached to one rod and driving a single crosshead/crank system. This verifies the tandem, common-rod nature of the design.

Why Other Options Are Wrong:
Set at 90° with separate cranks describes cross-compounding, not Woolf. Separate piston rods with independent cranks again imply cross-compound or twin arrangements. V-configuration is a different geometric layout not typical of the Woolf tandem form.

Common Pitfalls:
Confusing “Woolf/tandem compound” with “cross compound.” Remember: tandem (Woolf) shares a rod; cross-compound uses separate cranks (often 90° apart) on the same shaft.

Final Answer:
have common piston rod